Why did my Denoising disappeared?
It's now placed in the View Layer Properties, see screenshot. But actually I would use the Denoise node in the Compositor, because the Denoising option slows down the render and the result is inferior to the Denoise node from my experience.

Just plug it inbetween your render and the composite output, the result is usually far better than the Denoising even if you don't use any additional Denoising Data in the Normal and Albedo inputs.